the process of turning soymilk into tofu by adding nigari (magnesium chloride) or calcium sulfate. it is also achieved on a home scale by adding an acid such as vinegar or lemon juice to create a substitute for buttermilk in recipes.

and finally, it unintentionally happens when adding cold soymilk to hot coffee, which creates curdles and little tofu-y bits. (this can be avoided by putting the soymilk in the bottom of the mug and slowly adding the coffee to cook/acidify the soymilk slowly, which creates far smaller particles of tofu.)